Near-field RF charging pad with adaptive loading to efficiently charge an electronic device at any position on the pad

ABSTRACT

An example radio frequency (RF) charging pad includes: at least one processor for monitoring an amount of energy that is transferred from the RF charging pad to an RF receiver of an electronic device. The pad also includes: one or more transmitting antenna elements that are in communication with the processor for transmitting RF signals to the RF receiver. In some embodiments, each respective transmitting antenna element includes: (i) a conductive line forming a meandered line pattern; (ii) a first terminal of the conductive line for receiving current at a frequency controlled by the processor; and (iii) a second terminal coupled with a component that allows for modifying an impedance value at the second terminal. In some embodiments, the processor adaptively adjusts the frequency and/or the impedance value to optimize the amount of energy that is transferred from the one or more transmitting antenna elements to the RF receiver.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser. No. 62/433,227 filed Dec. 12, 2016, which is hereby incorporated by reference in its entirety.

This application is related to U.S. patent application Ser. No. 15/269,729, filed Sep. 19, 2016, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The embodiments herein generally relate to antennas used in wireless power transmission systems and, more specifically, to a near-field RF charging pad with adaptive loading to efficiently charge an electronic device at any position on the pad.

BACKGROUND

Conventional charging pads utilize inductive coils to generate a magnetic field that is used to charge a device. Users typically must place the device at a specific position on the charging pad and are unable to move the device to different positions on the pad, without interrupting or terminating the charging of the device. This results in a frustrating experience for many users as they may be unable to locate the device at the exact right position on the pad in which to start charging their device.

SUMMARY

Accordingly, there is a need for wireless charging systems (e.g., RF charging pads) that include adaptive antenna elements that are able to adjust energy transmission characteristics (e.g., impedance and frequency for a conductive line of a respective antenna element) so that the charging pad is capable of charging a device that is placed at any position on the pad. In some embodiments, these charging pads include one or more processors that monitor energy transferred from the transmitting antenna elements (also referred to herein as RF antenna elements or antenna elements) and to a receiver of an electronic device to be charged, and the one or more processors optimize the energy transmission characteristics to maximize energy transfer at any position on the charging pad. Some embodiments may also include a feedback loop to report received power at the receiver to the one or more processors. Such systems and methods of use thereof help to eliminate user dissatisfaction with conventional charging pads. By monitoring transferred energy, such systems and methods of use thereof help to eliminate wasted RF power transmissions by ensuring that energy transfer is maximized at any point in time and at any position at which a device may be placed on an RF charging pad, thus eliminating wasteful transmissions that may not be efficiently received.

In accordance with some embodiments, a radio frequency (RF) charging pad is provided. The RF charging pad includes: at least one processor for monitoring an amount of energy that is transferred from the RF charging pad to an RF receiver of an electronic device. The RF charging pad also includes: one or more antenna elements that are in communication with the one or more processors for transmitting RF signals to the RF receiver of the electronic device. In some embodiments, each respective antenna element includes: (i) a conductive line forming a meandered line pattern; (ii) a first terminal at a first end of the conductive line for receiving current that flows through the conductive line at a frequency controlled by the one or more processors; and (iii) a second terminal, distinct from the first terminal, at a second end of the conductive line, the second terminal coupled with a component that is controlled by the at least one processor and allows for modifying an impedance value at the second terminal. In some embodiments, the at least one processor is configured to adaptively adjust the frequency and/or the impedance value to optimize the amount of energy that is transferred from the one or more antenna elements to the RF receiver of the electronic device.

In accordance with some embodiments a method is also provided that is used to charge an electronic device through radio frequency (RF) power transmission. The method includes: providing a transmitter comprising at least one RF antenna. The method also includes: transmitting, via at the least one RF antenna, one or more RF signals and monitoring an amount of energy that is transferred via the one or more RF signals from the at least one RF antenna to an RF receiver. The method additionally includes: adaptively adjusting a characteristic of the transmitter to optimize the amount of energy that is transferred from the at least one RF antenna to the RF receiver.

Thus, wireless charging systems configured in accordance with the principles described herein are able to charge an electronic device that is placed at any position on the RF charging pad and avoid wasting energy by ensuring that energy transfer is constantly optimized.

Note that the various embodiments described above can be combined with any other embodiments described herein. The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not intended to circumscribe or limit the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the present disclosure can be understood in greater detail, a more particular description may be had by reference to the features of various embodiments, some of which are illustrated in the appended drawings. The appended drawings, however, merely illustrate pertinent features of the present disclosure and are therefore not to be considered limiting, for the description may admit to other effective features.

FIG. 1A is a high-level block diagram of an RF charging pad, in accordance with some embodiments.

FIGS. 1B-1C are high-level block diagrams showing a portion of an RF charging pad, in accordance with some embodiments.

FIG. 1D is a block diagram of a simplified circuit that illustrates energy flow within sections of an antenna element that is transmitting an RF signal, in accordance with some embodiments.

FIG. 2 is a schematic of a transmitting antenna element with two terminals, in accordance with some embodiments.

FIG. 3 is a flow chart of a method of charging an electronic device through radio frequency (RF) power transmission.

FIGS. 4A-4E are schematics showing various configurations for individual antenna elements within an RF charging pad, in accordance with some embodiments.

FIGS. 5A-5D are schematics of an antenna element for an RF receiver, in accordance with some embodiments.

FIG. 6 is a schematic of an RF charging pad with a plurality of transmitting antenna elements (or unit cells), in accordance with some embodiments.

In accordance with common practice, the various features illustrated in the drawings may not be drawn to scale. Accordingly, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may not depict all of the components of a given system, method or device. Finally, like reference numerals may be used to denote like features throughout the specification and figures.

DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the various described embodiments. However, it will be apparent to one of ordinary skill in the art that the various described embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure aspects of the embodiments.

FIG. 1A is a high-level block diagram of an RF charging pad, in accordance with some embodiments. As shown in FIG. 1A, some embodiments include a transmission pad 100 (also referred to herein as RF charging pad 100 or RF transmission pad 100). In some embodiments, the RF charging pad 100 includes one or more antenna elements that are each powered/fed by a respective power amplifier switch circuit 103 at a first end and a respective adaptive load terminal 102 at a second end (additional details and descriptions of the one or more antenna elements are provided below in reference to FIGS. 2A-2B).

In some embodiments, the RF charging pad 100 also includes (or is in communication with) a central processing unit 110 (also referred to here as processor 110). In some embodiments, the processor 110 is configured to control RF signal frequencies and to control impedance values at each of the adaptive load terminals 102 (e.g., by communicating with the load pick 106, which may be an application-specific integrated circuit (ASIC), to generate various impedance values). In some embodiments, the load pick 106 is an electromechanical switch that is placed in either an open or shorted state.

In some embodiments, an electronic device (e.g., a device that includes a receiver 104 as an internally or externally connected component, such as a remote that is placed on top of a charging pad 100 that may be integrated within a housing of a streaming media device or a projector) and uses energy transferred from one or more RF antenna elements of the charging pad 100 to the receiver 104 to charge a battery and/or to directly power the electronic device.

In some embodiments, the RF charging pad 100 is configured with more than one input terminal for receiving power (from power amplifier (PA) 108, FIG. 1A) and more than one output or adaptive load terminal 102. In some embodiments, the adaptive load terminals 102 at a particular zone of the RF charging pad 100 (e.g., a zone that includes antenna elements located underneath a position at which an electronic device (with an internally or externally connected RF receiver 104) to be charged is placed on the charging pad) are optimized in order to maximize power received by the receiver 104. For example, the CPU 110 upon receiving an indication that an electronic device with an internally or externally connected RF receiver 104 has been placed on the pad 100 in a particular zone 105 (the zone 105 includes a set of antenna elements) may adapt the set of antenna elements to maximize power transferred to the RF receiver 104. Adapting the set of antenna elements may include the CPU 110 commanding load pick 106 to try various impedance values for adaptive load terminals 102 that are associated with the set of antenna elements. For example, the impedance value for a particular conductive line at an antenna element is given by the complex value of Z=A+jB (where A is the real part of the impedance value and B is the imaginary part, e.g., 0+j0, 1000+j0, 0+50j, or 25+j75, etc.), and the load pick adjusts the impedance value to maximize the amount of energy transferred from the set of antenna elements to the RF receiver 104. In some embodiments, adapting the set of antenna elements also or alternatively includes the CPU 110 causing the set of antenna elements to transmit RF signals at various frequencies until a frequency is found at which a maximum amount of energy is transferred to the RF receiver 104. In some embodiments, adjusting the impedance value and/or the frequencies at which the set of antenna elements transmits causes changes to the amount of energy transferred to the RF receiver 104. In this way, the amount of energy transferred to the RF receiver 104 is maximized (e.g., to transfer at least 75% of the energy transmitted by antenna elements of the pad 100 to the receiver 104, and in some embodiments, adjusting the impedance value and/frequencies may allow up to 98% of the energy transmitted to be received by the receiver 104) may be received at any particular point on the pad 100 at which the RF receiver 104 might be placed.

In some embodiments, the CPU 110 determines that a maximum amount of energy is being transferred to the RF receiver 104 when the amount of energy transferred to the RF receiver 104 crosses a predetermined threshold (e.g., 75% or more of transmitted energy is received, such as up to 98%) or by testing transmissions with a number of impedance and/or frequency values and then selecting the combination of impedance and frequency that results in maximum energy being transferred to the RF receiver 104 (as described in reference to the adaptation scheme below).

In some embodiments, an adaptation scheme is employed to adaptively adjust the impedance values and/or frequencies of the RF signal(s) emitted from the RF antenna(s) 102 of the charging pad 100, in order to determine which combinations of frequency and impedance result in maximum energy transfer to the RF receiver 104. For example, the processor 110 that is connected to the charging pad 100 tries different frequencies (i.e., in the allowed operating frequency range or ranges) at a given location of the RF charging pad 100 (e.g., a zone or area of the RF charging pad 100 that includes one or more RF antenna elements for transmitting RF signals, such as zone 105 of FIG. 1A) to attempt to adaptively optimize for better performance. For example, a simple optimization either opens/disconnects or closes/shorts each load terminal to ground (in embodiments in which a relay is used to switch between these states), and may also cause RF antennas within the zone to transmit at various frequencies. In some embodiments, for each combination of relay state (open or shorted) and frequency, the energy transferred to the receiver 104 is monitored and compared to energy transferred when using other combinations. The combination that results in maximum energy transfer to the receiver 104 is selected and used to continue to transmitting the one or more RF signals to the receiver 104.

As another example, if five frequencies in the ISM band are utilized by the pad 100 for transmitting radio frequency waves and the load pick 106 is an electromechanical relay for switching between open and shorted states, then employing the adaptation scheme would involve trying 10 combinations of frequencies and impedance values for each antenna element 120 or for a zone of antenna elements 120 and selecting the combination that results in best performance (i.e., results in most power received at receiver 104, or most power transferred from the pad 100 to the RF receiver 104).

The industrial, scientific, and medical radio bands (ISM bands) refers to a group of radio bands or parts of the radio spectrum that are internationally reserved for the use of radio frequency (RF) energy intended for scientific, medical and industrial requirements rather than for communications. In some embodiments, all ISM bands (e.g., 40 MHz, 900 MHz, 2.4 GHz, 5.8 GHz, 24 GHz, 60 GHz, 122 GHz, and 245 GHz) may be employed as part of the adaptation scheme. As one specific example, if the charging pad 100 is operating in the 5.8 GHz band, then employing the adaptation scheme would include transmitting RF signals and then adjusting the frequency at predetermined increments (e.g., 50 MHz increments, so frequencies of 5.75 GHz, 5.755 GHz, 5.76 GHz, and so on). In some embodiments, the predetermined increments may be 5, 10 15, 20, 50 MHz increments, or any other suitable increment.

In some embodiments, the antenna elements 120 of the pad 100 may be configured to operate in two distinct frequency bands, e.g., a first frequency band with a center frequency of 915 MHz and a second frequency band with a center frequency of 5.8 GHz. In these embodiments, employing the adaptation scheme may include transmitting RF signals and then adjusting the frequency at first predetermined increments until a first threshold value is reached for the first frequency band and then adjusting the frequency at second predetermined increments (which may or may not be the same as the first predetermined increments) until a second threshold value is reached for the second frequency band. For example, the antenna elements 120 may be configured to transmit at 902 MHz, 915 MHz, 928 MHZ (in the first frequency band) and then at 5.795 GHz, 5.8 GHz, and 5.805 GHz (in the second frequency band).

Turning now to FIGS. 1B-1C, high-level block diagrams showing a portion of an RF charging pad are illustrated, in accordance with some embodiments.

FIG. 1B shows a schematic of a single TX antenna 120 (which may be a part of an array of such antennas, all forming the charging pad 100 that is shown in FIG. 1A). (In some embodiments, the TX antenna 120 is also referred to as a TX antenna element 120). In some circumstances, an RF receiving unit/antenna (RX) (or a device that includes the receiving unit 104 as an internally or externally connected component) is placed on top of a portion of the pad 100 that includes the TX antenna 120 (which includes a conductive line that forms a meandered line arrangement, as shown in FIG. 1B).

In some embodiments, the receiver 104 has no direct contact to a metallic conductive line of the single TX antenna 120 and is just coupled (i.e. in near-field zone) to the TX antenna 120.

In some embodiments, the TX antenna 120 has two or more terminals (or ports) that are labeled as 121 (which may be a respective one of the terminals 102 of FIG. 1A) and 123 (which may be connected to a respective one of the PA switch circuits 103 of FIG. 1A) in FIG. 1B. In some embodiments, the source of power (from the power amplifier or PA) is connected to terminal 123 and an adaptive load (e.g., an electromechanical switch or ASIC) is connected to terminal 121. In some embodiments, the adaptive load is formed generally as a complex impedance which may have both real and imaginary parts (i.e., a complex adaptive load can be formed using active devices (e.g., integrated circuits or chips made of transistors) or passive devices formed by inductors/capacitors and resistors). In some embodiments, the complex impedance is given by the formula Z=A+jB (e.g., 0+j0, 100+j0, 0+50j, and etc.), as discussed above.

In some embodiments, the receiver 104 may also be considered as a third terminal. To eliminate wasted energy, the receiver 104 should absorb a maximum amount (e.g., 75% or more, such as 98%) of the induced power that travels from terminal 123 and towards terminal 121. In some embodiments, processor 110 is connected to the receiver 104 through a feedback loop (e.g., by exchanging messages using a short-range communication protocol, such by BLUETOOTH low energy (BLE) to exchange messages). In some alternative embodiments, the feedback loop from the receiver back to the CPU at the transmitter may utilize a same frequency band as the power transmission signals transmitted by the pad 100, rather than using a separate communication protocol and/or a different frequency band.

In some embodiments, the feedback loop and messages exchanged may be used to indicate an amount of energy received or alternatively or additionally may indicate an increase or decrease in the amount of energy received as compared to previous measurements. In some embodiments, the processor 110 monitors the amount of energy received by the receiver 104 at certain points in time and controls/optimizes the adaptive load to maximize the power transferred from terminal 123 to terminal 121. In some embodiments, monitoring the amount of energy transferred includes one or both of (i) receiving information from the receiver 104 (or a component of an electronic device in which the receiver 104 is located) that indicates an amount of energy received by the receiver 104 at a certain point in time and (ii) monitoring an amount of energy that remains in the conductive line at terminal 121 (instead of having been absorbed by the receiver 104). In some embodiments, both of these monitoring techniques are utilized while, in other embodiments, one or the other of these monitoring techniques is utilized.

In some embodiments, the receiver 104 (i.e., an electronic device that includes the receiver 104 as an internally or externally connected component) may be placed anywhere on top of the charging pad 100 (i.e., partially or fully covering the conductive line that forms a meandered pattern on a respective antenna element 120) and the processor 110 will continue to monitor the amount of energy transferred and make needed adjustments (e.g., to impedance and/or frequency) to maximize the energy transferred to the receiver 104.

To help illustrate operation of the charging pad 100 and the antenna elements 120 included therein, the transmitting antenna element 120 shown in FIG. 1B as divided into two sections: 1) section 125 starts at the terminal 123 of the antenna element 120 and extends to an edge of the receiver 104; and 2) section 127 is formed by the rest of the transmitting antenna element 120 and the terminal 121. The blocks are described in more detail below with respect to FIG. 1C. It should be understood that sections 125 and 127 are functional representations used for illustrative purposes, and they are not intended to designate a specific implementation that partitions an antenna element into separate sections.

Turning now to FIG. 1C, a block diagram of the TX antenna 120 is shown. In some embodiments, an effective impedance value (Z_(effective)), starting from a point that divides sections 125 and 127 and ending at the TX antenna 120's connection to the adaptive load 106 (e.g., terminal 121) will change based on location of the receiver 104 on the TX antenna 120 and based on a selected load provided by adaptive load 106 at the terminal 121. In some embodiments, the selected load is optimized by the adaptive load 106 (in conjunction with the processor 110, FIG. 1A) to tune Z_(effective) in such a way that the energy transferred between terminal 123 and the receiver 104 reaches a maximum (e.g., 75% or more of energy transmitted by antenna elements of the pad 100 is received by the RF receiver 104, such as 98%), while energy transfer may also stay at a minimum from terminal 123 to terminal 121 (e.g., less than 25% of energy transmitted by antenna elements of the pad 100 is not received by the RF receiver 104 and ends up reaching terminal 121 or ends up being reflected back, including as little as 2%).

In embodiments in which an electromechanical switch (e.g., a mechanical relay) is used to switch between open and shorted states, moving the switch from the open to the shorted state (e.g., shorted to a ground plane) for a particular antenna element 120 causes the impedance value, Z_(effective), at a respective terminal 121 for that particular antenna element 120 to drop to a value close to 0 (alternatively, switching from the shorted to the open state causes the impedance value to jump close to a value close to infinity). In some embodiments, the frequency adaptation scheme discussed above in reference to FIG. 1A is employed to test various combinations of impedance values and RF signal frequencies, in order to maximize energy transferred to an RF receiver (e.g., receiver 104, FIGS. 1A-1C). In some embodiments, an integrated circuit (IC or chip) may be used instead of an electromechanical switch as the adaptive load 106. In such embodiments, the adaptive load 106 is configured to adjust the impedance value along a range of values, such as between 0 and infinity. In some embodiments, the IC may be formed by adaptive/reconfigurable RF active and/or passive elements (e.g., transistors and transmission lines) that are controlled by firmware of the IC (and/or firmware executing on the CPU 110 that controls operation of the IC). In some embodiments, the impedance produced by the IC, and controlled through firmware and based on information from the feedback loop (discussed above in reference to FIG. 1A), may be changed to cover any load values selected from a Smith Chart (or the IC may be designed to produce certain loads covering a portion of values form the Smith Chart). A Smith Chart may be sampled and stored in a memory (e.g., as a lookup table) that is accessible by the processor 110, and the processor 110 may perform lookups using the stored Smith Chart to determine various impedance values to test. For example, the integrated circuit may be configured to select a predetermined number of complex values (e.g., 5j to 10j, 100+0j, or 0+50j, etc.) for the impedance value to test in combination with various RF transmission frequencies, in order to locate a combination of values that optimizes energy transferred to the receiver 104 (examples of maximized energy transfer are discussed above).

FIG. 1D is a block diagram of a simplified circuit that illustrates energy flow within sections of an antenna element that is transmitting an RF signal, in accordance with some embodiments. The references to part1 and part2 in FIG. 1D refer to sections illustrated in FIGS. 1B and 1C, in particular, part1 corresponds to section 125 and part2 corresponds to section 127.

As shown in FIG. 1D, the effective impedance (Z_(effective)) for a transmitting antenna element 120 is formed by the portion of the conductive line that is after the receiver 104 (which, in some embodiments, forms a meandered line pattern as discussed in more detail below) and the adaptive load (labelled to as section 127 in FIGS. 1B and 1C). In some embodiments, by optimizing, the load Z_(effective) will be tuned so the energy transferred from PA to the receiver 104 is maximized; and, the energy remaining in the conductive line by the time it reaches the adaptive load is minimized (as discussed above).

FIG. 2 is a schematic of an antenna element with two terminals, in accordance with some embodiments. As shown in FIG. 2, an input or first terminal of the antenna element 120 (also described as terminal 123 in reference to FIGS. 1B-1D above) is connected with a power amplifier 108 and an output or second terminal (also described as terminal 121 in reference to FIGS. 1B-1D above) is connected with a component 106 that allows for configuring an adaptive load. Stated another way, in some embodiments, the antenna element 120 is fed by the power amplifier 108 from the first terminal and the antenna element 120 is also terminated at a second terminal at an adaptive load (for example, the mechanical relay that switches between shorted and open states).

In some embodiments, the charging pad 100 (FIG. 1A) is made of single-layer or multi-layer copper antenna elements 120 with conductive lines that form a meandered line pattern. In some embodiments, each of these layers has a solid ground plane as one of its layers (e.g., a bottom layer). One example of a solid ground plane is shown and labelled for the transmitting antenna element shown in FIG. 2.

In some embodiments, the RF charging pad 100 (and individual antenna elements 120 included therein) is embedded in a consumer electronic device, such as a projector, a laptop, or a digital media player (such as a networked streaming media player, e.g. a ROKU device, that is connected to a television for viewing streaming television shows and other content). For example, by embedding the RF charging pad 100 in a consumer electronic device, a user is able to simply place a peripheral device, such as a remote for a projector or a streaming media player (e.g., the remote for the projector or streaming media player includes a respective receiver 104, such as the example structures for a receiver 104 shown in FIGS. 5A-5D), on top of the projector or the streaming media player and the charging pad 100 included therein will be able to transmit energy to a receiver 104 that is internally or externally connected to the remote, which energy is then harvested by the receiver 104 for charging of the remote.

In some embodiments, the RF charging pad 100 may be included in a USB dongle as a standalone charging device on which a device to be charged is placed. In some embodiments, the antenna elements 120 may be placed near a top surface, side surfaces, and/or a bottom surface of the USB dongle, so that a device to be charged may be placed at various positions that contact the USB dongle (e.g., a headphone that is being charged might sit on top of, underneath, or hang over the USB dongle and would still be able to receive RF transmissions from the embedded RF charging pad 100).

In some embodiments, the RF charging pad 100 is integrated into furniture, such as desks, chairs, countertops, etc., thus allowing users to easily charge their devices (e.g., devices that includes respective receivers 104 as internally or externally connected components) by simply placing them on top of a surface that includes an integrated RF charging pad 100.

Turning now to FIG. 3, a flow chart of a method 300 of charging an electronic device through radio frequency (RF) power transmission is provided. Initially, a transmitter is provided 302 that includes at least one RF antenna (e.g., antenna element 120, FIGS. 1B-1D and 2) for transmitting one or more RF signals or waves, i.e., an antenna designed to and capable of transmitting RF electromagnetic waves. In some embodiments, an array of RF antenna elements 120 are arranged adjacent to one another in a single plane, in a stack, or in a combination of thereof, thus forming an RF charging pad 100. In some embodiments, the RF antenna elements 120 each include an antenna input terminal (e.g., the first terminal 123 discussed above in reference to FIG. 2) and an antenna output terminal (e.g., the second terminal 121 discussed above in reference to FIG. 2).

In some embodiments, a receiver (e.g., receiver 104, FIGS. 1A-1D) is also provided 304. The receiver also includes one or more RF antennas for receiving RF signals 310. In some embodiments, the receiver includes at least one rectenna that converts 318 the one or more RF signals into usable power to charge a device that includes the receiver 104 as an internally or externally connected component. In use, the receiver 104 is placed 306 within a near-field radio frequency distance to the at least one antenna. For example, the receiver may be placed on top of the at least one RF antenna or on top of a surface that is adjacent to the at least one RF antenna, such as a surface of a charging pad 100.

One or more RF signals are then transmitted 308 via at the least one RF antenna. The system is then monitored 312/314 to determine the amount of energy that is transferred via the one or more RF signals from the at least one antenna to a RF receiver (as is also discussed above). In some embodiments, this monitoring 312 occurs at the transmitter, while in other embodiments the monitoring 314 occurs at the receiver which sends data back to the transmitter via a back channel (e.g., over a wireless data connection using WIFI or BLUETOOTH). In some embodiments, the transmitter and the receiver exchange messages via the back channel, and these messages may indicate energy transmitted and/or received, in order to inform the adjustments made at step 316.

In some embodiments, a characteristic of the transmitter is adaptively adjusted 316 to attempt to optimize the amount of energy that is transferred from the at least one RF antenna to the receiver. In some embodiments, this characteristic is a frequency of the one or more RF signals and/or an impedance of the transmitter. In some embodiments, the impedance of the transmitter is the impedance of the adjustable load. Also in some embodiments, the at least one processor is also configured to control the impedance of the adaptive load. Additional details and examples regarding impedance and frequency adjustments are provided above.

In some embodiments, the transmitter includes a power input configured to be electrically coupled to a power source, and at least one processor (e.g., processor 110, FIGS. 1A-1B) configured to control at least one electrical signal sent to the antenna. In some embodiments, the at least one processor is also configured to control the frequency of the at least one signal sent to the antenna.

In some embodiments, the transmitter further comprises a power amplifier electrically coupled between the power input and the antenna input terminal (e.g., PA 108, FIGS. 1A, 1C, 1D, and 2). Some embodiments also include an adaptive load electrically coupled to the antenna output terminal (e.g., terminal 121, FIGS. 1A-1C and 2). In some embodiments, the at least one processor dynamically adjusts the impedance of the adaptive load based on the monitored amount of energy that is transferred from the at least one antenna to the RF receiver. In some embodiments, the at least one processor simultaneously controls the frequency of the at least one signal sent to the antenna.

In some embodiments, each RF antenna of the transmitter includes: a conductive line forming a meandered line pattern, a first terminal (e.g., terminal 123) at a first end of the conductive line for receiving current that flows through the conductive line at a frequency controlled by one or more processors, and a second terminal (e.g., terminal 121), distinct from the first terminal, at a second end of the conductive line, the second terminal coupled to a component (e.g., adaptive load 106) controlled by the one or more processors and that allows for modifying an impedance value of the conductive line. In some embodiments, the conductive line is disposed on or within a first antenna layer of a multi-layered substrate. Also in some embodiments, a second antenna is disposed on or within a second antenna layer of the multi-layered substrate. Finally, some embodiments also provide a ground plane disposed on or within a ground plane layer of the multi-layered substrate.

FIGS. 4A-4E are schematics showing various configurations for individual antenna elements within an RF charging pad, in accordance with some embodiments. As shown in FIGS. 4A-4E, an RF charging pad 100 (FIG. 1A) may include antenna elements 120 that are made using different structures.

For example, FIGS. 4A-4B show examples of structures for an antenna element 120 that includes multiple layers that each include conductive lines formed into meandered line patterns. The conductive lines at each respective layer may have the same (FIG. 4B) or different (FIG. 4A) widths (or lengths, or trace gauges, or patterns, spaces between each trace, etc.) relative to other conductive lines within a multi-layer antenna element 120. In some embodiments, the meandered line patterns may be designed with variable lengths and/or widths at different locations of the pad 100 (or an individual antenna element 120), and the meandered line patterns may be printed on more than one substrate of an individual antenna element 120 or of the pad 100. These configurations of meandered line patterns allow for more degrees of freedom and, therefore, more complex antenna structures may be built that allow for wider operating bandwidths and/or coupling ranges of individual antenna elements 120 and the RF charging pad 100.

Additional example structures are provided in FIGS. 4C-4E: FIG. 4C shows an example of a structure for an antenna element 120 that includes multiple layers of conductive lines forming meandered line patterns that also have sliding coverage (in some embodiments, respective meandered line patterns may be placed in different substrates with just a portion of a first meandered line pattern of a respective substrate overlapping the a second meandered line pattern of a different substrate (i.e., sliding coverage), and this configuration helps to extend coverage throughout width of the antenna structure); FIG. 4D shows an example of a structure for an antenna element 120 that includes a conductive line having different lengths at each turn within the meandered line pattern (in some embodiments, using different lengths at each turn helps to extend coupling range of the antenna element 120 and/or helps add to the operating bandwidth of the RF charging pad 100); and FIG. 4E shows an example of a structure for an antenna element 120 that includes a conductive line that forms two adjacent meandered line patterns (in some embodiments, having a conductive line that forms two adjacent meandered line patterns helps to extend width of the antenna element 120). All of these examples are non-limiting and any number of combinations and multi-layered structures are possible using the example structures described above.

FIGS. 5A-5D are schematics of an antenna element for an RF receiver, in accordance with some embodiments. In particular FIGS. 5A-5D show examples of structures for RF receivers (e.g., receiver 104, FIGS. 1A-1D and 2), including: (i) a receiver with a conductive line that forms meandered line patterns (the conductive line may or may not be backed by solid ground plane or reflector), as shown in FIGS. 5A (single-polarity receiver) and 5B (dual-polarity receiver). FIGS. 5C-5D show additional examples of structures for an RF receiver with dual-polarity and a conductive line that forms a meandered line pattern. Each of the structures shown in FIGS. 5A-5D may be used to provide different coupling ranges, coupling orientations, and/or bandwidth for a respective RF receiver. As a non-limiting example, when the antenna element shown in FIG. 5A is used in a receiver, very small receivers may be designed/built that only couple to the pad 100 in one direction. As another non-limiting example, when the antenna elements shown in FIGS. 5B-5D are used in a receiver, the receiver is then able to couple to the pad 100 in any orientation.

Commonly-owned U.S. patent application Ser. No. 15/29,729 also provides additional examples and descriptions of meandered line patterns for antenna elements (e.g., those shown in FIGS. 2A-2D, 3, 4, 5, 7, 8, and 9A-9B, and described in the specification) and descriptions of the functioning of power transfer systems that include antenna elements with meandered line patterns (e.g., paragraphs [0022]-[0034] and FIGS. 1A-1B), and the disclosure of this commonly-owned application thus supplements the descriptions of antenna elements with meandered line patterns provided herein (for both receivers and transmitters, or a combination thereof).

FIG. 6 is a schematic of an RF charging pad with a plurality of transmitting antenna elements (unit cells) that form a larger RF charging/transmitting pad, in accordance with some embodiments. In some embodiments, the RF charging pad 100 is formed as an array of adjacent antenna elements 120 (the distance between cells may be optimized for the best coverage). In some embodiments, when a receiver is placed in an area/gap that is between adjacent antenna elements 120, attempts to optimize energy transfer (e.g., in accordance with the adaptation scheme discussed above in reference to FIG. 1A) may not result in increased energy transfer above an acceptable threshold level (e.g., 75% or more). As such, in these circumstances, adjacent antenna elements may both be configured to transmit RF waves at full power at the same time to transfer additional energy to a receiver that is placed on a surface of the RF charging pad, and at a location that is between adjacent antenna elements 120.

As one possible configuration in accordance with some embodiments, port (or terminal) group #1 (FIG. 6) supplies power, port (or terminal) groups #2 and #3 provide adaptive loads (e.g., an electromechanical relay moving between short-circuit and open-circuit states). As another example of a suitable configuration, port (or terminal) groups #1, #2 and #3 may also be used to supply power via a power amplifier to the charging pad 100 (at the same time or with one group at a time being switched when necessary).

In some embodiments, each transmitting antenna element 120 of the RF charging pad 100 forms a separate coupling zone which is controlled by a feeding (PA) terminal and one or more terminals to support adaptive load(s), as explained in detail above. In some embodiments, feedback from the receiver helps determine the zone on top of which the receiver is placed, and this determination activates that zone. In circumstances in which the receiver is placed between two or more zones (e.g., at an area/gap that is between adjacent antenna elements 120), additional adjacent zones might be activated to ensure sufficient transfer of energy to the receiver.

The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.

It will also be understood that, although the terms “first,” “second,” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first region could be termed a second region, and, similarly, a second region could be termed a first region, without changing the meaning of the description, so long as all occurrences of the “first region” are renamed consistently and all occurrences of the “second region” are renamed consistently. The first region and the second region are both regions, but they are not the same region.

The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 

What is claimed is:
 1. A radio frequency (RF) charging pad, comprising: at least one processor for monitoring an amount of energy that is transferred from the RF charging pad to an RF receiver of an electronic device; and one or more transmitting antenna elements that are in communication with the one or more processors for transmitting RF signals to the RF receiver of the electronic device, each respective transmitting antenna element including: a conductive line forming a meandered line pattern; a first terminal at a first end of the conductive line for receiving current that flows through the conductive line at a frequency controlled by the one or more processors; and a second terminal, distinct from the first terminal, at a second end of the conductive line, the second terminal coupled with a component that is controlled by the at least one processor and allows for modifying an impedance value at the second terminal, wherein the at least one processor is configured to adaptively adjust the frequency and/or the impedance value to optimize the amount of energy that is transferred from the one or more transmitting antenna elements to the RF receiver of the electronic device.
 2. The RF charging pad of claim 1, wherein the electronic device is placed on top of a surface of the RF charging pad.
 3. The RF charging pad of claim 1, wherein the component is a mechanical relay coupled with the second terminal for switching the second terminal between open and short states, and the impedance value is adaptively adjusted at the second terminal of the respective transmitting antenna element by opening or closing the mechanical relay to switch between an open or short circuit, respectively.
 4. The RF charging pad of claim 1, wherein the component is an application-specific integrated circuit (ASIC), and the impedance value is adaptively adjusted by the ASIC along a range of values.
 5. The RF charging pad of claim 1, wherein adaptively adjusting the frequency includes adjusting the frequency in predetermined increments.
 6. The RF charging pad of claim 1, wherein the one or more processors are configured to adaptively adjust the frequency and/or impedance includes by adaptively adjusting the frequency and the impedance value to determine a maximum amount of energy that is transferred to the RF receiver of the electronic device, and once the maximum amount of energy is determined, transmitting the RF signals at the frequency and the impedance value that resulted in the maximum amount of energy transfer to the RF receiver.
 7. The RF charging pad of claim 1, wherein the at least one processor monitors the amount of energy that is transferred to the RF receiver based at least in part on information received from the electronic device, the information identifying energy received at the RF receiver from the RF signals.
 8. The RF charging pad of claim 7, wherein the information received from the electronic device identifying received energy is sent using a short-range communication protocol.
 9. The RF charging pad of claim 8, wherein the short-range communication protocol is bluetooth low energy (BLE).
 10. The RF charging pad of claim 1, wherein the one or more processors monitor the energy transferred based at least in part on an amount of energy that is detected at the second terminal.
 11. A method of charging an electronic device through radio frequency (RF) power transmission, the method comprising: providing a charging pad that includes a transmitter comprising at least one RF antenna, wherein the at least one RF antenna comprises: a conductive line forming a meandered line pattern; a first terminal at a first end of the conductive line for receiving current that flows through the conductive line at a frequency controlled by the at least one processor; and a second terminal, distinct from the first terminal, at a second end of the conductive line, the second terminal coupled to a component controlled by the at least one processor, the component configured to modify an impedance value at the second terminal; transmitting, via the at least one RF antenna, one or more RF signals; monitoring an amount of energy that is transferred via the one or more RF signals from the at least one RF antenna to an RF receiver; and adaptively adjusting a characteristic of the transmitter to optimize the amount of energy that is transferred from the at least one RF antenna to the RF receiver, wherein the characteristic is selected from a group consisting of (i) a frequency of the one or more RF signals, (ii) an impedance of the transmitter, and (iii) a combination of (i) and (ii).
 12. The method of claim 11, wherein the at least one RF antenna is part of an array of RF antennas, and the transmitter further comprises: a power input configured to be electrically coupled to a power source; and at least one processor configured to control at least one electrical signal sent to the at least one RF antenna.
 13. The method of claim 12, wherein the at least one processor is also configured to control the frequency of the at least one electrical signal sent to the at least one RF antenna.
 14. The method of claim 11, wherein the conductive line is disposed on or within a first antenna layer of a multi-layered substrate.
 15. The method of claim 14, wherein a second RF antenna is disposed on or within a second antenna layer of the multi-layered substrate.
 16. The method of claim 15, wherein a ground plane is disposed on or within a ground plane layer of the multi-layered substrate.
 17. The method of claim 11, wherein the RF receiver includes at least one rectenna that converts the one or more RF signals into power to charge a device that is connected to the RF receiver.
 18. The method of claim 11, further comprising, prior to the transmitting, locating the RF receiver within a near-field radio frequency distance to the at least one RF antenna. 